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Silicon Graphics Image

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Silicon Graphics Image
Filename extension
.sgi (among others)
Internet media type
image/sgi[1]
Type code'.SGI'
Magic number01 DA
Developed byPaul Haeberli
Initial release0.95 / 1995; 30 years ago (1995)[2][3]
Latest release
1.00
1996; 29 years ago (1996)
Type of formatimage file
StandardSGI Image File Format[4]

Silicon Graphics Image (SGI) or the RGB file format is the native raster graphics file format for Silicon Graphics workstations.[3] The format was invented by Paul Haeberli.[3] It can be run-length encoded (RLE). FFmpeg and ImageMagick, among others, support this format.

Background

Common file extensions are:

.sgi or .rgb
3 colour channels
.rgba
3 colour channels and alpha
.bw or .int
black and white
.inta
black and white and alpha

This format was originally developed for IRIX. The master files of the SVT High Definition Multi Format Test Set are SGIs.[5][6][7] Frame 200 of the ParkJoy sequence in this set (15722.sgi, 3840×2160, 47.4 MB) was used in WebP comparisons.

Technical Details

Field number Length Field name Description
1 2 byte File signature/magic number For show file is SGI file
2 1 byte Compression Whether use RLE compress or no
3 1 byte Bytes per pixel channel 1 for 8 bit channel or 2 for 16 bit channel
4 2 bytes Dimension Image dimension, equal 3 for RGBA image
5 2 bytes X size Image width
6 2 bytes Y size Image height
7 2 bytes Number of channels Number channel in image, equal 4 for RGBA image
8 4 bytes Minimum pixel value Smallest pixel value in image
9 4 bytes Maximum pixel value Largest pixel value in image
10 4 bytes Dummy No use, ingore
11 80 bytes Image name C string name have last byte equal 0x00
12 4 bytes Color map ID Only for color map image
13 404 bytes Dummy For make head 512 bytes long. Ignore

File Signature/Magic Number

Should equal 0x01 0xda for SGI file.

Compression

If no compression equal 0; 1 for RLE compression.

Bytes Per Pixel Channel

Value is 1 for 8 bit per channel (most image); 2 for 16 bits per channel.

Dimension

Value equal 1 for 1 channel, 1 scanline image ; 2 for 1 channel, many scanline image (); 3 for many channel, many scanline image (most image).

X Size

Scanline width of image.

Y Size

Number of scanlines in image.

Numer Of Channels

Number channels in image. Grey scale image is 1; RGB is 2; RGBA is 3. SGI can have more than 4 channels.

Minimum Pixel Value

Smallest pixel value in all channels. Because SGI use unsigned char or short for channels, smallest value can have is zero.

Maximum pixel value

Largest pixel value in all channels. Because SGI use unsigned char or short for channels, largest value can have for 8 bit/channel is 0xff; 16 bit/channel image is 0xffff.

Dummy

4 bytes not use.

Image name

Image name is 80 bytes (maximum 79 characters ≠ 0x00) C string. If name is shorter than 79 characters, all bytes after equal 0x00 for fill all 80 bytes.

Color Map ID Have 4 types:

  1. 0x00 normal
  2. 0x01 dithered
  3. 0x02 screen
  4. 0x03 colormap

Dummy 404 bytes for header 512 bytes long.

See also

References

  1. ^ .sgi MIME type not registered at IANA
  2. ^ Paul Haeberli (1996). "The SGI Image File Format 0.97". Silicon Graphics. Retrieved 2014-03-07.[dead link] Alt URL
  3. ^ a b c "SGI Image File Format File Format Summary". Encyclopedia of Graphics File Formats, Second Edition. O'Reilly. April 1996. ISBN 1-56592-161-5. Retrieved 2014-03-07. {{cite web}}: Unknown parameter |authors= ignored (help)
  4. ^ Paul Haeberli (1996). "The SGI Image File Format 1.00". Silicon Graphics. Retrieved 2014-03-07.
  5. ^ Lars Haglund (Feb 2006). "The SVT High Definition Multi Format Test Set" (PDF). SVT. Retrieved 2014-02-23.
  6. ^ "SVT_MultiFormat/2160p50_CgrLevels_Master_SVTdec05". Video Quality Experts Group (VQEG). 2006. Retrieved 2014-03-01.
  7. ^ High-Quality Visual Experience: Creation, Processing and Interactivity of High-Resolution and High-Dimensional Video Signals. Signals and Communication Technology. Springer. 2010. pp. 147–154. ISBN 978-3-642-12802-8. LCCN 2010925849. {{cite book}}: Unknown parameter |authors= ignored (help)
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